spec_context.clj

(ns spec-context
  (:require [clojure.spec :as s]))

(defmulti node-spec ::fancy?)
(defmethod node-spec true [_] ::fancy-node)
(defmethod node-spec :default [_] ::boring-node)

(s/def ::node (s/multi-spec node-spec ::fancy?))

(s/def ::fancy? boolean?)
(s/def ::children (s/every ::node))

(s/def ::boring-node (s/keys :req [::children]))
(s/def ::fancy-node (s/keys :req [::children ::flair]))

(s/def ::flair number?)


(defn make-fancy [node]
  (-> node
      (update ::children #(mapv make-fancy %))
      (assoc ::fancy? true)))

(comment

  (def boring {::children [{::children []}]})
  (def fancy {::flair 1 ::children [{::flair 2 ::children []}]})
  (def invalid {::flair 1 ::children [{::children []}]})

  (make-fancy boring)

  ;; All fine.
  (s/explain ::node boring)
  (s/explain ::node fancy)
  (s/explain ::node invalid)

  (s/explain ::node (make-fancy fancy))   ; Good!
  (s/explain ::node (make-fancy invalid)) ; No good, nested!
  (s/explain ::node (make-fancy boring))  ; No good, two places!

)